1. Field of the Invention
The present invention relates to a water-treatment separating membrane manufactured by dropping droplets of an organic solution including an acyl halide compound onto an aqueous amine solution layer formed on a porous support.
2. Description of the Related Art
The movement of a solvent between two solutions separated by a semi-permeable membrane, from a solution having a lower concentration of a solute to another solution having a higher concentration of a solute, is known as osmosis. Pressure applied to the solution having the higher concentration of the solute by the movement of the solution is known as osmotic pressure. When a level of external pressure, higher than osmotic pressure, is applied, the solvent may move from the solution having the higher concentration of the solute to the solution having the lower concentration of the solute. This phenomenon is known as reverse osmosis. By using the principle of reverse osmosis, various salts and organic materials may be separated by the semi-permeable membrane by using a pressure gradient as a driving force. A water-treatment separating membrane is used for separating materials on the molecular level, removing salts from saline water and seawater, and providing water for domestic, commercial and industrial uses by using the reverse osmosis phenomenon.
The most important function required for the water-treatment membrane includes the exhibition of the high level of salt rejection with respect to the separating membrane and the maintenance of the high permeation flux of a solvent at a relatively low pressure. To accomplish the above-described conditions, a water-treatment separating membrane having good salt rejection performance while maintaining high permeation flux has been suggested, by forming a thin film of an active polyamide layer for removing salts on a porous support for maintaining mechanical strength of the separating membrane (U.S. Pat. No. 4,277,344). More particularly, the water-treatment separating membrane is manufactured by forming a minute and porous support through forming a polysulfone layer on a non-woven fabric, impregnating the minute and porous support with an aqueous m-phenylenediamine (mPD) solution to form an aqueous amine solution layer, and impregnating the minute and porous support with an organic solution including trimesoyl chloride (TMC) so that the mPD contacts the TMC to allow interfacial polymerization and to form a polyamide layer. According to the above-described method, since a polar solvent, water and a non-polar organic solution contact, the polymerization of mPD and TMC occurs only at the interface therebetween. Thus, a very thin polyamide active layer may be formed.
However, since the above-suggested water-treatment separating membrane has a fast decreasing degree of chlorine resistance with time, the replacement period of the membrane is short. To retard the decreasing degree of the chlorine resistance of the water-treatment separating membrane, a method of increasing a specific surface area of an active layer has been suggested. Japanese Unexamined Patent Publication No. Hei 10-337454 discloses a method of increasing the specific surface area of the skin layer of a water-treatment separating membrane by forming an active layer and impregnating the active layer with an acid solution to form embossing or winkles on the skin layer. Korean Unexamined Patent Publication No. 1998-0068304 discloses a method of increasing surface roughness by post-treating a reverse osmosis composite layer with a strong acid.
However, as disclosed in Japanese Unexamined Patent Publication No. Hei 10-337454, in the case of impregnating a separating membrane including the active layer in the acid solution, the surface of the separating membrane may exhibit an anionic charge, and a contaminating material exhibiting a cationic charge may attach to the separating membrane, thereby decreasing the transmittance of the separating membrane. Thus, a separate post-treatment process of coating the surface of the separator with an electrically neutral polymer is necessary.
In addition, according to the method disclosed in Korean Unexamined Patent publication No. 1998-0068304, a polyamide composite layer is acid treated to overcome the defects concerning the generation of the anionic charge on the surface of the separating membrane and to increase the surface roughness. Then, the surface is secondly coated with an aqueous amine solution and a halide compound. Thus, a separate post-treatment process is also necessary.